1. Field of the Invention
The present invention relates to an embedding structure for a blade mounted in a rotating machine.
2. Description of the Related Art
In general, gas turbines incorporate a compressor for feeding compressed air to a combustor. The compressor includes a compressor rotor disposed thereinside, the rotor rotating about a central axis of the gas turbine. The compressor further includes a compressor blade embedded in a compressor disk fixed to the rotor.
The blade of a gas turbine compressor in operation undergoes a centrifugal force produced from weight of the blade itself and a large pressure load on a high pressure side. An exciting force arising from irregular pressure variations that occur during starting may therefore cause a vibrational stress to act on a blade dovetail portion, so that the blade dovetail portion may be damaged through fatigue.
Conventionally, an entire blade load bearing surface of the blade dovetail bears load of the foregoing types. A high stress, however, occurs at an end portion of contact between the blade load bearing surface and a rotor load bearing surface of the rotor. In addition to the high stress occurring, the point of contact develops fretting damage caused by wear, resulting at times in reduced reliability in fatigue strength.
JP-2008-69781-A (FIGS. 3 and 5) discloses a technique for avoiding reduction in the fatigue strength reliability by making an undercut (a stress relief groove) that includes three parts of a large radius portion, a small radius portion, and a straight line portion at an intersection portion between a neck portion and a pressure surface.